Dual non-contacting mechanical face seal having concentric seal faces

ABSTRACT

A mechanical seal for providing fluid sealing between a housing and a rotatable shaft includes a first seal ring having a first seal face and a second seal ring having a second seal face. The first seal face further has a first portion and a second portion and the seal faces of the first and second seal rings are opposed to each other when assembled. The first seal ring or the second seal ring is adapted to rotate with the rotatable shaft, and the other seal ring is restrained from rotating. The seal faces are configured to produce a primarily hydrostatic fluid force between at least a portion of the first portion of the first seal face and at least a portion of the second seal face. In addition, the seal faces are configured to produce a hydrodynamic fluid force and a hydrostatic fluid force between at least a portion of the second portion of the first seal face and at least a portion of the second seal face.

REFERENCE TO RELATED APPLICATIONS

This application is a cont. of Ser. No. 09/013,089 filed Jan. 26, 1998,now U.S. Pat. No. 6,076,830 which application is a continuation in partof U.S. patent application Ser. No. 09/005,957, filed on Jan. 9, 1998andentitled “Dual Non-Contacting Mechanical Face Seal Having ConcentricSeal Faces” which is now abandoned; which is a continuation in part ofU.S. patent application Ser. No. 08/992,753, filed on Dec. 17, 1997, nowU.S. Pat. No. 6,131,912, and entitled “Split Mechanical Face Seal”; U.S.patent application Ser. No. 08/992,751, filed on Dec. 17, 1997, now U.S.Pat. No. 6,068,264, and entitled “Split Mechanical Face Seal withNegative Pressure Control System”; U.S. patent application Ser. No.08/992,611, filed on Dec. 17, 1997, now U.S. Pat. No. 6,059,293, andentitled “Split Mechanical Face Seal With Fluid Introducing Structure”;and U.S. patent application Ser. No. 08/992,613, filed on Dec. 17, 1997,now U.S. Pat. No. 6,068,263, and entitled “Split Mechanical Face SealWith Resilient Pivoting Member”. Each of the above-referenced patent isincorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to seals for providing fluidsealing between a housing and a rotating shaft. More particularly, theinvention relates to mechanical face seals in which a fluid isintroduced between portions of the seal faces of the seal.

Conventional mechanical seals are employed in a wide variety ofmechanical apparatuses to provide a pressure-tight and a fluid-tightseal between a rotating shaft and a stationary housing. The seal isusually positioned about the rotating shaft, which is mounted in andprotrudes from the stationary housing. The seal is typically bolted tothe housing at the shaft exit, thus preventing loss of pressurizedprocess fluid from the housing. Conventional mechanical seals includeface type mechanical seals, which include a pair of annular sealingrings that are concentrically disposed about the shaft, and axiallyspaced from each other. The sealing rings each have seal faces that arebiased into physical contact with each other. Usually, one seal ringremains stationary, while the other ring contacts the shaft and rotatestherewith. The mechanical seal prevents leakage of the pressurizedprocess fluid to the external environment by biasing the seal ringsealing faces into physical contact with each other. As a result of therepeated physical contact between the faces, abrasion of the seal facesoccurs and the seals typically exhibit undesirable wear characteristicsand leakage.

The prior art attempted to overcome the above difficulties by employingnon-contact mechanical seals that utilize a fluid interposed between theseal ring faces to reduce frictional wear. Conventional mechanicalnon-contact face seals typically employ pumping grooves, such as spiralor Raleigh step grooves, formed in one of the seal faces of the sealrings to develop a hydrodynamic lifting force that separates the sealfaces. The resultant gap allows fluid to be disposed between the sealfaces to prevent rubbing and abrasion of the seal faces.

Conventional non-contacting face seals, however, exhibit drawbacks insome areas of performance that are less than optimal. For example, innon-contacting seal designs, which rely primarily upon rotation toprovide hydrodynamic separation of the seal faces, a substantial amountof seal face abrasion can occur during start-up operation or duringperiods when the shaft is rotating at low speeds. For this reason, theseconventional non-contacting type mechanical face seals are unsuitablefor low speed operation or for conditions which require frequentstarting and stopping of the shaft.

In order to overcome the problems associated with purely hydrodynamicnon-contacting seals, combination hydrostatic and hydrodynamic sealshave been designed. Such combination seals typically rely on fluidpressure to provide hydrostatic separation and rotation to providehydrodynamic separation of the seal faces. The performance of suchcombination seals has been less than optimal because the thickness ofthe fluid gap formed between the seal faces varies significantlydepending upon rotation speed. Such conventional combination mechanicalseals exhibit a substantial difference in fluid film thickness betweenhydrostatic (i.e., non-rotating) and hydrodynamic (rotating) operationdue to the significant pumping force provided by the spiral grooves. Thelarger gap formed between the seal faces at high rotation speeds allowsfor greater leakage across the seal faces than would otherwise bedesirable.

A significant number of conventional non-contacting seals employ a dualseal arrangement in which three or more seals rings are arranged axiallyalong the shaft. Such dual seals can be arranged in a back-to-back,face-to-face, or tandem configuration and typically employ a highpressure barrier fluid at the outer diameter of the seal rings whilemaintaining the process fluid at the inner diameter of the seal rings.The barrier fluid is introduced to the seal faces through pumpinggrooves formed in one of the seal faces.

Dual non-contacting seals have also proven to be less than optimal in annumber of areas of performance. Sealing the process fluid at the innerdiameter of the seal can result in dirt or other particles within theprocess fluid becoming clogged between the seal faces, interfering withthe operation of the seal. In addition, upon loss of the barrier fluidpressure, some dual seal designs do not maintain a fluid-tight seal,resulting in leakage of the process fluid. The additional seals rings indual seals also result in an exceedingly bulky seal that is oftenunsuitable for applications in which the axially space along the shaftis limited. Furthermore, dual seals typically require modification ofthe housing to accommodate the increased size of the seal, resulting incomplex and costly installation and servicing of the seal.

As the above described and other prior art seals have proven less thanoptimal, an object of the present invention is to provide an improvednon-contacting mechanical face seal that is operable under a wider rangeof operating conditions.

Another object of the present invention is to provide a non-contactingmechanical face seal that maintains a fluid-tight seal that is lessdependent on shaft speed.

Still another object of the present invention is to provide anon-contacting mechanical seal that minimizes seal face contact at lowershaft speeds and is suitable for applications requiring frequentstarting and stopping of the shaft.

Yet another object of the present invention is to provide anon-contacting mechanical face seal that is compact in design and can beinstalled without modification of the housing.

A further object of the present invention is to provide a non-contactingmechanical seal that can provide the benefits of hydrostatic andhydrodynamic operation simultaneously.

Another object of the present invention is to provide a non-contactingmechanical seal having a sealing structure that alleviates O-ringhysteresis.

Other general and more specific objects of this invention will in partbe obvious and will in part be evident from the drawings and thedescription which follow.

SUMMARY OF THE INVENTION

These and other objects of the present invention are attained by amechanical seal of the present invention which provides fluid sealingbetween a housing and a rotatable shaft and is suitable for operationover a wide range of operating conditions, including at low shaftspeeds. The seal is preferably a non-contacting seal that provides forhydrostatic operation over a portion of one of the seal faces andhydrostatic and hydrodynamic operation over another portion of the sealfaces. Accordingly, the mechanical seal of the present invention allowsfor partial or complete separation of the seal faces independent ofshaft speed by having a portion of the seal faces exposed solely to ahydrostatic fluid force. Thus, contact between the seal faces atstart-up or at low shaft speeds can be minimized or eliminated therebyreducing wear on the seal faces. Additionally, the mechanical seal ofthe present invention provides the advantages of hydrodynamic operationat higher shaft speeds, thereby increasing the overall range ofeffective operating conditions for the seal.

In a preferred embodiment, the mechanical seal of the present inventionincludes a first seal ring having a first seal face and a second sealring having a second seal face. The first seal face further has a firstportion and a second portion. The seal faces of the first and secondseal rings are opposed to each other when assembled. One of the sealrings is adapted to rotate with the rotating shaft, and the other sealring is restrained from rotating. The seal faces are configured toproduce a primarily hydrostatic fluid force between at least a portionof the first portion of the first seal face and at least a portion ofthe second seal face. In addition, the seal faces are configured toproduce a hydrodynamic fluid force and a hydrostatic fluid force betweenat least a portion of the second portion of the first seal face and atleast a portion of the second seal face.

Preferably, the first seal ring has a first outer radially extendingseal face at the first portion of the first seal face and a second innerradially extending seal face at the second portion of the first sealface. The first outer seal face and the second inner seal face aregenerally co-planar. Preferably, the second seal face is sized tooverlap at least a portion of the inner and outer seal faces of thefirst seal ring, thus the seal rings are capable of generating thehydrostatic and the hydrodynamic forces as a result of dam portionsformed by the seal face overlap. The first outer seal face can bedisposed along an outer circumferential portion of the first seal faceand the second inner seal face can be disposed along an innercircumferential portion of the first seal face to form a dual concentricseal on a single seal ring.

The mechanical seal of the present invention preferably employs aplurality of pumping grooves formed in the second portion of the firstseal face to produce the hydrodynamic fluid force between at least aportion of the second portion of the first seal face and at least aportion of the second seal face. Barrier fluid can be introduced to theplurality of pumping grooves formed in the first seal face such that thepumping grooves and the fluid generate the hydrodynamic and thehydrostatic fluid forces between the first and second seal faces toseparate selectively at least a portion of the first seal face from atleast a portion of the second seal face.

In a preferred embodiment, a plurality of passages can be formed withinthe second seal ring to introduce barrier fluid to the pumping groovesformed in the first seal face. Each passage can open onto the secondseal face at one end and can be in fluid communication with a fluidsource at another end. A circumferential groove can also be formed inthe second seal face and can be positioned on the second seal face suchthat the passages open onto the circumferential groove. Thecircumferential groove and the passages are preferably in registrationwith at least a portion of the pumping grooves formed in the first sealface, such that the passages and the circumferential groove providefluid to the pumping grooves to generate the hydrodynamic fluid force.

In a preferred embodiment, the seal of the present invention can alsoinclude a fluid control system for controlling the separation of theseal faces by adjusting the pressure of the barrier fluid introduced tothe grooves. Preferably, the fluid control system adjusts the thicknessof the gap formed between the seal faces by adjusting the barrier fluidpressure over the process fluid pressure during operation of the seal.

The mechanical seal of the present invention can include a sleeve forsecuring the first seal ring to the rotating shaft. The sleeve has aflanged end and is sized for mounting generally concentrically about therotating shaft. The seal can also include an annular lock ring mountedconcentrically about the sleeve for securing the sleeve, and thus thefirst seal ring, to the rotating shaft. The lock ring can include aplurality of apertures formed therein for receiving fasteners whichfrictionally engage the rotating shaft to secure the lock ring and thesleeve to the shaft.

The mechanical seal of the present invention can also include a glandassembly sized for mounting to the housing and about the shaft. Thegland assembly can be coupled to the second seal ring to connect thesecond seal ring to the housing and, thus, restrain the second seal ringfrom rotating. The gland assembly can include an axial inner gland plateand an axial outer gland plate. A resilient member, such as an O-ring,can be interposed between the inner gland plate and the outer glandplate to form a seal therebetween.

A resilient member, such as a an O-ring, can be interposed between thesecond seal ring and the gland assembly to provide a seal between thesecond seal ring and the gland assembly. A compression member can alsobe provided for axially and radially biasing the resilient member intocontact with the second seal ring and the gland assembly. Thecompression member is preferably an annular compression plate having anannular inner flanged portion for engaging the resilient member. Theinner flanged portion can include an axially and radially extendingangled surface for axially and radially biasing the resilient memberinto contact with the second seal ring and the gland assembly.

The mechanical seal of the present invention can optionally include asystem for introducing a closing fluid to a rear surface of the secondseal ring to provide a closing force on the second seal ring. Theclosing force preferably acts upon a portion the second seal faceoverlapping the second portion of the first seal face. The closing fluidsystem can include a fluid conduit formed in the outer gland plate thatopens proximate the rear surface of the second seal ring at one end andis in fluid communication with a fluid source at another end.Preferably, a common fluid supply provides both the closing fluid to theclosing fluid system and barrier fluid for introduction to the sealfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bemore fully understood by reference to the following detailed descriptionin conjunction with the attached drawings in which like referencenumerals refer to like elements through the different views. Thedrawings illustrate principals of the invention and, although generallyor occasionally not to scale, may show relative dimensions.

FIG. 1 is a fragmentary view in cross-section of a non-contactingmechanical face seal according to the teachings of the presentinvention;

FIG. 2 is an exploded unassembled view of the seal components of thenon-contacting mechanical face seal of FIG. 1 according to the teachingsof the present invention;

FIG. 3 is an exploded unassembled view, from a different perspectivethan FIG. 2, of the seal components of the non-contacting mechanicalseal of FIG. 1 according to the teachings of the present invention;

FIG. 4 is a perspective view of the inner gland plate of thenon-contacting mechanical face seal of FIG. 1 according to the teachingsof the present invention;

FIG. 5 is a perspective view of the outer gland plate of thenon-contacting mechanical face seal of FIG. 1 according to the teachingsof the present invention;

FIG. 5A is a side elevational view in cross-section of the outer glandplate of FIG. 5 according to the teachings of the present invention;

FIG. 5B is a partial side elevational view in cross-section of the outergland plate of FIG. 5 showing the stationary seal ring and thecompression plate seated within the outer gland plate;

FIG. 5C is a partial side elevational view in cross-section of the outergland plate of FIG. 5 showing the stationary seal ring and a secondembodiment of the compression plate seated within the outer gland plate;

FIG. 6 is a perspective view of the sleeve for supporting the rotaryseal ring of the non-contacting mechanical face seal of FIG. 1 accordingto the teachings of the present invention;

FIG. 7 is a perspective view of the rotary seal ring of the of thenon-contacting mechanical face seal of FIG. 1 according to the teachingsof the present invention;

FIG. 7A is a side elevational view in cross-section of the rotary sealring of FIG. 7;

FIG. 8 is a perspective view of the stationary seal ring of thenon-contacting mechanical face seal of FIG. 1 according to the teachingsof the present invention;

FIG. 8A is a side elevational view in cross-section of the stationaryseal ring of FIG. 8;

FIG. 9 is a perspective view in cross-section of the stationary sealring of FIG. 8 according to the teachings of the present invention;

FIG. 10 is a perspective view of the compression plate of thenon-contacting mechanical face seal of FIG. 1 according to the teachingsof the present invention;

FIG. 10A is a side elevational view of the compression plate of FIG. 10;

FIG. 11 is a perspective view of the lock ring of the non-contactingmechanical face seal of FIG. 1 according to the teachings of the presentinvention;

FIG. 12 is a fragmentary view in cross-section of the non-contactingmechanical face seal of FIG. 1 of the invention with a pressure feedbacksystem mounted within the gland;

FIG. 13 is a fragmentary view in cross section of the non-contactingmechanical face seal of FIG. 12 employing an alternate embodiment of thepressure feedback system;

FIGS. 14A and 14B are side elevational, diagrammatic views incross-section of the rotary and stationary seal rings of thenon-contacting mechanical face seal of FIG. 1, illustrating the variousforces acting on the seal rings according to the teachings of thepresent invention.

FIG. 15 is a side elevational, diagrammatic view in cross-section of therotary and stationary seal rings of the non-contacting mechanical faceseal of FIG. 1, illustrating the various forces acting on the seal ringsduring a loss of barrier fluid pressure condition according to theteachings of the present invention.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

A mechanical face seal 10 in accordance with the present invention isshown in FIGS. 1, 2 and 3. The illustrated mechanical face seal 10 isconcentrically disposed about a shaft 12 and is secured to an externalwall of a fluid housing 11, such as a pump or the like. The shaft 12extends along an axis 13, and is mounted, at least partially, in thehousing 11. The seal 10 is constructed to provide fluid sealing betweenhousing 11 and shaft 12, thereby preventing a process medium or fluidfrom escaping the housing 11. Fluid sealing is achieved by a stationaryseal ring 14 and a rotary seal ring 16, each ring having a radiallyextending arcuate seal face 18 and 20, respectively, as shown in FIGS. 7and 8. The seal face 18 of the stationary seal ring 14 is biased into asealing relationship with the seal face 20 of the seal ring 16, asdescribed in greater detail below. Thus, these individual seal surfacesform a fluid seal operable under a wide range of operating conditionsand in a wide range of services, as described in greater detail below.

A similar seal is described in U.S. Pat. No. 6,155,572, filed on Jan.26, 1998 and entitled “Non-Contacting Mechanical Face Seal IncludingFluid Control System”; and in U.S. Pat. No. 6,120,034, filed on Jan. 26,1998 and entitled “Secondary Sealing Assembly for Mechanical Face Seal”,both of which are incorporated herein by reference.

The terms “process medium” and “process fluid” used herein generallyrefer to the medium or fluid being transferred through the housing 11.In pump applications, for example, the process medium is the fluid beingpumped through the pump housing.

The terms “axial” and “axially” used herein refer to a directiongenerally parallel to shaft axis 13. The terms “radial” and “radially”used herein refer to a direction generally perpendicular to shaft axis13.

The mechanical seal 10 is preferably a mechanical non-contacting-typeface seal in which a barrier fluid is introduced between the seal faces18, 20 of the first and second seal rings 14, 16, respectively.Preferably, the barrier fluid used with the present seal is a gas. In anon-contacting-type mechanical face seal the barrier fluid acts tominimize, inhibit or prevent contact between substantial radial portionsof the seal face 18 and radial portions of the seal face 20, therebyreducing the frictional engagement and the resulting wear of the sealfaces 18, 20. Accordingly, a non-contacting-type mechanical face sealincludes seal designs in which there is total separation of the sealfaces at all times, total separation of the seal faces under certainconditions, i.e., during periods of shaft rotation, and occasional orpartial separation of the seal faces. In contrast, a contacting-typeface seal includes seal designs in which partial or complete contact ofthe seal faces is maintained. In both types of seals, the barrier fluidfunctions as a heat transfer medium to transfer heat away from the sealfaces to reduce the effects of thermal stress on the seal faces.

With reference to FIGS. 1 through 5, the illustrated mechanical seal 10includes, in addition to the stationary seal ring 14 and the rotary sealring 16, a seal gland assembly 30 and a rotary seal ring sleeve 100. Theseal gland assembly 30 includes a pair of gland plates, an inner glandplate 34 and an outer gland plate 36. The inner gland plate 34 isconcentrically disposed about the shaft 12 and is positioned adjacentthe housing 11 for connection thereto. The outer gland plate 36 ispositioned axially adjacent along axis 13 and substantially parallel tothe inner gland plate 34.

Referring to FIG. 4, the inner gland plate 34 has a radial inner surface38 and a radial outer surface 40, as well as an axial inner surface 42and an axial outer surface 44. The inner axial surface 42 is positionedproximate the housing 11 and has a housing gasket groove 48 formedtherein adjacent the inner radial surface 38, as best illustrated inFIG. 1. The groove 48 seats a flat, annular housing gasket 50 thatpreferably has an axial dimension greater than the depth of the groove48, thereby providing a pressure-tight and a fluid-tight seal betweenthe mechanical seal 10 and the housing 11. The housing gasket 50 ispreferably mounted in the groove 48 and secured thereto by an adhesive.This arrangement helps to prevent leakage of the process medium alongthe mating portions of the mechanical seal 10 and the housing 11 whenmounted together.

Referring again to FIGS. 1 through 4, an annular inner gland platesealing portion or collar 52 extends axially outwardly from the outersurface 44 and includes a radially extending surface 54. The radiallyextending surface 54 of the inner gland plate sealing portion 52 isdimensioned to abut a gland plate O-ring 56 to provide sealing betweenthe inner gland plate 34 and the outer gland plate 36 when the glandplates are mounted together.

The outer gland plate 36 has an axially extending inner surface 58 andan axially extending outer surface 60, as well as a radially extendinginner surface 62 and a radially extending outer surface 64, as shown inFIGS. 1-3, 5 and 5A. Beginning from the outer surface 60, the radialinner surface 62 includes a first radially extending surface portion 66and a second radially extending surface 68 that is stepped radiallyinwardly from the first radially extending surface 66. A gland gasketgroove 70 is formed in the second radially extending surface 68 adjacentthe first radially extending surface 66. An axially extending firstsurface 72 connects the second radially extending surface 68 and a thirdradially inwardly extending surface 74. An axially extending secondsurface 76 connects the third radially extending surface 74 and a fourthradially extending surface 78.

A stationary seal ring receiving chamber 90 is formed by the firstsurface 72, the third radially extending surface 74, and the secondsurface 76 of the stationary seal ring 14, as illustrated in FIG. 5A. Agroove 92 is formed in the first surface 72 to seat an elastomericmember 94, such as an O-ring, for sealing against the stationary sealring member 14.

The gland plate O-ring 56 is seated within the gland gasket groove 70 ofthe outer gland plate 36. When the gland plates 34 and 36 are assembled,the radially extending surface 54 of the inner gland plate sealingportion abuts and compresses the gland plate O-ring 56 into the glandgasket groove 70. In this manner, gland plate O-ring 56 functions toform a fluid-tight and a pressure-tight seal between the gland plates.Furthermore, the outer diameter of the annular collar 52 is slightlysmaller than the outer diameter of the groove 70, such that whenassembled, the collar 52 outer surface is closely disposed to or mateswith the radially outer wall of the groove 70.

Each of the gland plates 34 and 36 include four fastener recesses 80 toaccommodate bolts (not shown) to mount mechanical seal 10 of theinvention to the housing 11. Alternatively, bolt-tabs may be providedabout the periphery of the seal 10 to facilitate connection of the seal10 to the housing 11. Examples of suitable bolt tabs are shown in U.S.Pat. No. 5,209,496 and U.S. Pat. No. 5,571,268, both of which areassigned to the assignee hereof and are incorporated herein byreference. Each of the gland plates also include two fastening apertures82 to accommodate bolts 84 for coupling the inner gland plate 34 to theouter gland plate 36.

As illustrated in FIGS. 1 through 3 and 6, a rotary seal ring sleeve 100is disposed within the inner chamber formed by the gland assembly 30.The rotary seal ring sleeve 100 includes an axially-extending,cylindrical sleeve body 102 having an axial outer end 104 and an axialinner end 106, as well as an outer surface 108 and an inner surface 110.The outer surface 108 of the sleeve 100 includes a first outer surface112 proximate the outer end 104 and a second outer surface 114 proximatethe inner end 106 and stepped radially outward from the first outersurface 112. In a preferred embodiment, the outer diameter of the firstouter surface 112 is less than the diameter of the inner radial surface58 of the outer gland plate 36. This clearance allows the sleeve 100 toseat within the gland assembly 30 for unobstructed rotational movementtherein.

The diameter of the inner surface 110 of the sleeve 100 is preferablyequal to or slightly greater than the diameter of the shaft 12, to whichthe sleeve 100 is to be attached, as illustrated in FIG. 1. The innersurface 110 has formed thereon an annular channel 116 for mounting ashaft gasket 118. When mounted in the channel 116, the gasket 118sealingly mates with the shaft 12, providing a fluid-tight seal alongthe sleeve and the shaft interface, FIG. 1.

Referring to FIGS. 1 and 6, a flange 120 extends radially outwardly fromthe sleeve body 102 proximate to the axially inner end 106. The flange120 has an axially inner surface 122 and an axially outer surface 124. Aradial outer surface 126 extends axially between the inner surface 122and the outer surface 124. Preferably, the diameter of the outer surface126 is less than the diameter of the inner radial surface 38 of theinner gland plate 34. This clearance allows the flange 120 to seatwithin the gland assembly 30 for unobstructed rotational movementtherein.

The outer surface 124 has an annular groove 128 formed therein forreceiving an elastomeric sealing member 130, such as an O-ring, asdescribed in more detail below. A first outer surface 132 is steppedaxially outward from the outer surface 124 of the sleeve 100 and islocated radially inward from the annular groove 128.

A plurality of bores 134 are formed through the flange 120, each one ofwhich receives one end of a drive pin 136, as illustrated in FIGS. 1 and6. The other end of the drive pin 136 is received in a correspondingslot 138 in the rotary seal ring 16. The drive pins 136 operate toimpart rotational motion to the rotary seal ring 16.

The axial outer end 104 of the sleeve 100 includes a plurality ofvariously sized fastener-receiving apertures 140 that mount screws 142,as illustrated in FIGS. 2, 3, and 6. The screws are mounted to thesleeve 100 through a lock ring 144, as shown in FIG. 11. The screws 142are provided to radially and axially secure the sleeve 100, and thus therotary seal ring 16, to the shaft 12 for rotation therewith.

The rotary seal ring sleeve 100, the gland assembly 30, and the lockring 144 can be formed from any suitably rigid material, such as, forexample, stainless steel or other metal alloys.

With reference to FIGS. 1 through 3, 7 and 7A, the rotary seal ringassembly 16 includes an arcuate inner surface 162. The inner surface 162includes a first axially extending surface 164 extending axially fromthe seal face 20 of the rotary seal ring 16. The inner diameter of thefirst surface 164 of the rotary seal ring is preferably greater than orequal to the diameter of the second outer surface 114 of the sleeve topermit mounting of the rotary seal ring upon the sleeve. A radiallyextending connecting wall 168 connects the first surface 164 to a secondsurface 166. The second surface 166 of the rotary seal ring 16 isstepped radially outward from the first surface 164 to accommodate anelastomeric centering member 170, such as an O-ring. The elastomericcentering member 170 seats against the second surface 166 and theconnecting wall 168 of the rotary seal ring, as well as the second outersurface 114 of the sleeve 100, to center the rotary seal ring 16 aboutthe sleeve 100.

The rotary seal ring includes a substantially smooth, arcuate axiallyextending outer surface 172. The diameter of the outer surface 172 ispreferably less than the diameter of the inner surface 38 of the innergland plate 34.

The rotary seal ring 16 includes a rear surface 174 extending radiallybetween the outer surface 172 and the inner surface 166. Elastomericsealing member 130 sealingly abuts the outer surface 174 of the rotaryseal ring 16 and seats within the annular groove 128 to form afluid-tight, pressure-tight seal between the rotary seal ring and thesleeve. The first outer surface 132 of the sleeve 100 also abuts therear surface 174 of the rotary seal ring. The first outer surface 132functions to provide additional supporting of the rotary seal ring onthe sleeve and limits the amount of compression of the elastomeric sealring 130, as well as controlling pivoting or coning of the rotary sealring under pressure.

The illustrated seal face 20 of the rotary seal ring segments has aplurality of pumping grooves 180 formed therein, as is best shown inFIG. 7. The term “pumping groove” is used herein to denote any type ofsurface recess formed in one or the other or both of the seal ringswhich functions in combination with a fluid to generate lifting pressurefields, such as hydrodynamic lifting forces, between the seal faces. Thepumping grooves can include any suitable recess configuration, such asspiral grooves and Raleigh step-type grooves, that operate incombination with a fluid to lift and separate the seal faces from eachother during use. According to a preferred embodiment, the illustratedgrooves are spiral-type grooves that are dependent on shaft speed toseparate hydrodynamicly the seal faces. For the sake of clarity, thegrooves are hereinafter called spiral grooves, although it is to beunderstood that other types of grooves can be employed. In a preferredembodiment, the spiral grooves 180 are radially disposed between theinner surface 162 and the outer surface 172 of the rotary seal ring 16.The spiral grooves 180 accordingly split the rotary seal ring seal face20 into two concentric seal faces 20 a and 20 b. In this manner a dualseal having separate concentric seal faces 20 a and 20 b on a singleseal ring is formed. Referring to FIG. 7A, the first concentric sealface 20 a begins at the outer surface 172 and extends to the outerradial edge of the spiral grooves 180. The second concentric seal face20 b extends from either the inner radial edge of the spiral grooves 180to the inner surface 162 of the rotary seal ring, or in an alternatepractice, from the outer radial edge of the spiral grooves 180 to theinner surface 162. The second seal face 20 b can thus include the spiralgrooves 180 and the land or dam portion of the seal face 20 disposedradially inward from the spiral grooves. According to a preferredembodiment, the concentric seals are co-planar.

When assembled, the stationary seal ring 14 and the rotary seal ring 16are substantially aligned such that the seal face 18 overlies or isdisposed in registration with at least a portion of the seal face 20 a,the spiral grooves 180, and the seal face 20 b. This arrangement formsdam portions or lands on either side of the grooves 180 that helpcontrol or regulate the leakage of fluid through the seal faces 18, 20.According to the illustrated embodiment, the seal face 18 of thestationary seal ring 14 overlies a significant portion of the firstconcentric seal face 20 a and a significant portion of the secondconcentric seal face 20 b.

With reference to FIG. 1, the grooves 180 communicate with the seal face18 of the stationary seal ring 14. A barrier fluid at a specifiedregulated pressure P_(b), generally greater than the process pressureP_(p) and the ambient pressure P_(a), is introduced to the grooves 180through barrier fluid conduits 228 formed in the stator seal ring 14, asdescribed in further detail below. The barrier fluid acts to provide aseparation force on the seal faces 18 and 20. The separation forceoperates to minimize, inhibit, or prevent contact between radialportions of the seal face 18 and radial portions of the seal faces 20 aand 20 b, thereby reducing the frictional engagement and the resultingwearing of the seal faces 18, 20 a and 20 b.

The type of separation force formed between the seal faces variesradially across the rotary seal face 20. At the first seal face 20 a,the separation force is primarily or generally completely a hydrostaticseparation force. The terms “hydrostatic separation force” and“hydrostatic force” used herein refer to a force having a magnitude thatis independent of the shaft rotation speed and is at least partially andpreferably significantly dependent upon the magnitude of any pressuredifferential developed across the area upon which the force is acting.Accordingly, the magnitude of the primarily hydrostatic separation forceacting upon seal face 20 a, as well as the corresponding portion of theseal face 18, is at least partially dependent upon the magnitude of thepressure differential between the barrier fluid pressure P_(b) and theprocess fluid pressure P_(p) across the seal face 20 a and isindependent of the speed at which the shaft 12 and thus the rotary sealring 16 rotates.

The separation force developed between the rotary seal ring second sealface 20 b, which for purposes of this discussion includes the spiralgrooves 180, and the stationary seal ring seal face 18 includes bothhydrostatic and hydrodynamic force components. The terms “hydrodynamicseparation force” and “hydrodynamic force” used herein refer to a forcehaving a magnitude that is dependent upon the relative velocity of theseal faces. Accordingly, the magnitude of the separation force actingupon the second seal face 20 b, as well as the corresponding portion ofthe seal face 18, is dependent upon at least two factors: the pressuredifferential between the barrier fluid pressure P_(b) and the ambientfluid pressure P_(a) across the seal face 20 b (the hydrostaticcomponent); and the velocity at which the rotary seal ring seal face 20b rotates relative to the stationary seal ring face 18, i.e., the shaftrotation speed (the hydrodynamic component). The hydrodynamic componentof the separation force acting on the rotary seal ring second seal face20 b is generated by the pressure differential created by the pumpingaction of the spiral grooves 180 in a manner that is known in the art.Those of ordinary skill will recognize that the force distribution canbe reversed, that is, the primarily hydrostatic force can be locatedalong the inner diameter, e.g., along seal face 20 b, and thehydrostatic and hydrodynamic forces can be located along the outerdiameter, e.g., along seal face 20 a. One of ordinary skill willrecognize that this reverse arrangement may require modification of thegroove configuration, as well as changing of the radial location of thebarrier fluid conduits on the stationary seal ring seal face 18. Thisreverse arrangement is particularly suitable for seal applications wherethe process fluid is disposed along the inner diameter rather than theouter diameter.

A significant advantage of the force distribution feature of themechanical seal 10 of the present invention is that it allows foradjustment of seal face contact and thus adjustment of the gap thicknessformed between the seal faces 18 and 20, prior to start-up, i.e., priorto shaft rotation. By increasing the barrier fluid pressure P_(b) overthe process fluid pressure P_(p), and thus the pressure differentialacross the seal faces, a hydrostatic separation force can be produced atboth the first and second seal faces 20 a and 20 b of the rotary sealring. Because the closing force on seal face 20 a is only applied byprocess fluid pressure P_(p), as described below, the degree of sealface contact, i.e., the magnitude of the gap between the seal faces, canthus be controlled by adjusting the barrier fluid pressure P_(b) betweenthe seal faces prior to start-up or at low and substantially lowrotation speeds. In this manner, contact between the seal faces 18, and20 a, and 20 b at start-up or at low shaft speeds can be minimized oreliminated thereby reducing wear on the seal faces. Accordingly, theseal of the present invention provides the benefits of hydrostaticoperation at low shaft speeds, while concomitantly providing thehigh-speed benefits of hydrodynamic operation.

A further advantage of the seal of the present invention is that theseal is not limited to any specific spiral groove configuration. Forexample, the spiral grooves 180 can be uni-directional or bi-directionalgrooves. As is known in the art, uni-directional grooves allow for sealface separation only in one direction of shaft rotation, whilebi-directional grooves permit separation in both directions of rotation.Examples of suitable spiral groove designs are described in U.S. Pat.Nos. 3,499,653, 4,889,348, 5,143,384 and 5,529,315, all of which areincorporated herein by reference. The illustrated spiral groove is aunidirectional groove that pumps barrier fluid from the high pressureprocess region of the seal located along the groove 234 of thestationary seal ring 14 to the lower pressure region located along theinner diameter of the rings. Those of ordinary skill will readilyrecognize that the illustrated seal can also be used with bi-directionalgrooves, common types of which are known in the art.

As shown in FIGS. 1, 8, 8A, and 9, the stationary seal ring 14 has anaxially extending inner surface 202 and an axially extending outersurface 204. The outer surface 204 includes a first outer surface 206that extends axially from the stationary seal ring face 18, as well as afurther axially extending second outer surface 208 that is steppedradially inward from the first outer surface 206. The first outersurface 206 and the second outer surface 208 form in combinationtherewith a first annular connecting wall 210 that extends radiallybetween the first and second outer surfaces.

The inner surface 202 includes a first inner surface 212 that extendsaxially from the stationary seal ring face 18, as well as a furtheraxially extending second inner surface 214 that is stepped radiallyinward from the first inner surface 206. The first inner surface 212 andthe second inner surface 214 form in combination therewith a firstannular connecting wall 216 that extends radially between the first andsecond inner surfaces. A third inner surface 218 extends axially to arear surface 220 and is stepped radially inward from the second innersurface 214. A second connecting wall 222 connects the second innersurface 214 and the third inner surface 218 and includes a radiallyextending section 224 and a beveled section 226.

The inside diameter of the first inner surface 212 of the stationaryseal ring 14 is greater than the diameter of the first outer surface 112of the sleeve 100, and is greater than the diameter of the first innersurface 164 of the rotary seal ring 16, thereby allowing motion of boththe shaft 12, the sleeve 100 and the rotary seal 16 relative to thestationary seal ring 14. The elastomeric member 94 seats within theouter gland plate groove 92 and abuts the second outer surface 208. Asecond elastomeric member 236 is positioned to abut the beveled section226 and the radially extending section 224 of the connecting wall 222 ofthe stationary seal ring 14, as well as the second surface 76 of theouter gland plate 36. The second elastomeric member 236 is biased intosealing contact with the inner surface 222 of the stationary seal ring14 and the second surface 76 of the outer gland plate 36, as describedin greater detail below. The elastomeric members 94 and 236 function toform fluid-tight and pressure-tight seals between the outer gland plate36 and the stationary seal ring 14, when the stationary seal ring ispositioned within stationary seal ring receiving chamber 90. Thestationary seal ring 14 is preferably composed of a carbon or ceramicmaterial.

With reference to FIGS. 1, 8, 8A, and 9, a plurality of barrier fluidbores 228 are formed in the stationary seal ring 14. The bores 228include an axially extending section 230 that extends axially from therear surface 220 and a diagonal section 232 that communicates with andextends from the axial section 230 to a continuous, circumferentialgroove 234 formed in the seal face 18. Barrier fluid from a barrierfluid supply, not shown, is introduced to the seal surfaces 18, 20 ofthe seal rings and the grooves 180 formed in the seal face 20 throughthe bores 228 and the groove 234.

One skilled in the art will recognize that the barrier fluid bores arenot limited to the number or shape described and illustrated herein. Forexample, a single barrier fluid bore can be provided. Likewise, theposition and arrangement of the barrier fluid bores is not limited tothose specifically disclosed herein, as alternative positions andarrangements are possible to achieve the same results. For example, thebarrier fluid bores can be formed in rotary seal ring 16, as well a thestationary seal ring 14, and can extend from the seal faces to any outersurface of the seal rings. In addition, the barrier fluid bore canextend linearly from the seal faces 18, 20 to an outer surface of theseal ring.

As best shown in FIGS. 1, 5A and 5B, each axial section 230 of thebarrier fluid bores 228 opens at the rear surface 220 of the stationaryseal ring 14 to provide fluid communication between the bores 228 and asimilar radial barrier fluid bore 240 formed in the outer gland plate36. The bore 240 formed in the outer gland plate 36 opens at one end atthe outer surface 60 of the gland assembly and at the other end at thefirst surface 72 of the outer gland plate 36. Barrier fluid from abarrier fluid supply (not shown) is supplied through the gland bore 240to each of the stationary seal ring segment bores 228.

A plurality of stationary sealing ring bores 252 are formed within theouter gland plate 36, each one of which receives one end of a retainingpin 250, as illustrated in FIG. 1. The other end of each of the pins 250is received in the axial section 230 of one of the barrier fluid bores228 of the stationary seal ring 14. The outer diameter of each of thepins 250 is preferably less than the inner diameter of the axial section230 of the barrier fluid bores 228 such that barrier fluid can flowaround the retaining pins 250. The pins 250 operate to prevent rotationof the stationary seal ring 14 within the outer gland plate 36.

With reference to FIGS. 1, 2, 5B, 5C, 10 and 10A, a secondary sealingassembly 301 is provided and is mounted on the backside of thestationary sealing ring 14 within the closing fluid chamber 280. Thesecondary sealing assembly 301 forms a fluid seal between the outergland plate 36 and two fluid environments, a process fluid chamber 290and an ambient fluid chamber 295, as best illustrated in FIG. 1. Thesecondary seal assembly 301 permits axial movement of the stationaryseal ring 14 when under pressure while concomitantly preventing leakageof fluid between the process fluid chamber 290, the ambient fluidchamber 295, and the closing fluid chamber 280. The secondary sealingassembly 301 includes one or more, and preferably a plurality, ofmechanical springs 270, a spacer or compression plate 300, and theelastomeric member 236. The springs 270 are disposed within spring bores272 formed within the outer gland plate 36, as illustrated in FIGS. 1,5B, and 5C. The mechanical springs 270 abut the compression plate 300which in turn abuts elastomeric member 236.

The mechanical springs 270 function to provide an axial force, throughthe compression plate 300 and the elastomeric member 236, forresiliently supporting the stationary seal ring 14 to bias thestationary seal ring such that the stationary and rotating seal faces 18and 20 are biased towards each other. As illustrated in FIG. 1, the sealring 14 is floatingly and non-rigidly supported in spaced relationrelative to the rigid walls and faces of the gland plates. This floatingand non-rigid support and spaced relationship permits small radial andaxial floating movements of the stationary seal ring 14 with respect tothe gland, while still allowing the rotary seal face 20 to follow and tobe placed into a sealing relationship with stationary seal ring face 18.

The compression plate 300 includes an inner radial surface 302 and anouter radial surface 304, as best illustrated in FIGS. 5B, 10 and 10A.The diameter of the outer surface 304 of the compression plate 300 ispreferably less than the diameter of the first surface 72 of the outergland plate 36. It is also preferable for the diameter of the innersurface 302 of the compression plate to be greater than the diameter ofthe second surface 76 of the outer gland plate 6. The compression plate300 further includes a front surface 306 and a rear surface 307. Thefront surface 306 has a radially extending first front surface 308. Aconnecting wall 310 extends axially between the first front surface 308and a multi-angled or beveled second front surface 311. The connectingwall 310 and the first front surface 308 form a generally right angletherebetween.

An elastomeric member receiving chamber 91 is formed by the radiallyextending section 224, beveled section 226, and the inner section 218 ofthe stationary seal ring; the multi-angled front surface 311 of thecompression plate 300; and the gland plate second surface 76, as bestillustrated in FIG. 5B. The chamber 91 is sized to accommodate theelastomeric member 236 without requiring an overly tight or compressivefit between the stationary seal ring 14 and the gland 30. Specifically,the elastomeric member receiving chamber 91 is sized to allow for thethermal expansion of the elastomeric member 236 without a significantincrease in the compressive force on the elastomeric member,particularly the radial inward component of the compressive force.Preferably, the chamber 91 is dimensioned larger than thepre-compression or pre-stressed (i.e. relaxed) cross-sectional area ofthe elastomeric member 236.

The increased size of chamber 91 relative to the elastomeric member 236avoids excessively compressing or squeezing the elastomeric member in amanner that could produce large frictional forces between theelastomeric member 236 and the outer gland plate surface 76.Particularly, the configuration of the chamber 91 allows the elastomericmember 236 to expand radially outward, i.e. in the direction of theinner section 218 of the stationary seal ring, when subjected to thermalstress during the operation of the seal. The freedom of expansion in theradial direction inhibits significant increases in compressive forces onthe elastomeric member 236, particularly in the radial direction, duringoperation of the seal. Thus, the radial inward force on elastomericmember 236 that seats the elastomeric member against the surface 76 ofthe outer gland plate remains substantially constant during theoperation of the seal. This in turn permits the axial frictional forcebetween the elastomeric member 236 and the outer gland plate surface 76to also be maintained at a substantially constant value duringoperation, because the magnitude of the axial frictional force isdependent on the magnitude of radial inward force on the elastomericmember. The elastomeric member 236 is thus not pre-disposed tofrictionally “hanging up” axial motion of the stationary seal ring 14.

Continuing to refer to FIG. 5B, the multi-angled front surface 311 ofthe compression plate 300 is a contacting surface which directly biasesthe elastomeric member 236 into sealing contact with the outer glandplate 36 and the stationary seal ring 14, and includes a plurality,preferably two, angled surfaces 312 and 314. The angled surfaces 312,314 are transverse to each other and arranged to form an oblique angleor a right angle, and preferably an obtuse angle. The front surface 314extends radially between the front inner surface 302 and the secondfront surface 312. According to a preferred practice, the angled frontsurfaces 312 and 314 directly abut the elastomeric member 236 when thecompression plate 300 is seated within the closing fluid chamber 280.Retaining pin bores 316 are formed in the compression plate 300 topermit the stationary seal ring retaining pins 250 to pass therethrough.The illustrated assembly and configuration of the compression plate 300eliminates the need for a second resilient or compliant component tohelp bias the elastomeric member in a selected direction to attain adesired compression.

The mechanical springs 270 are coupled to the rear surface 307 of thecompression plate 300 to axially bias the compression plate into contactwith the elastomeric member 236, as best illustrated in FIG. 5B. Thesprings 270, through the plate 300, provides a closing force on thestationary seal ring that urges the stationary seal ring 14 toward therotary seal ring 16. The angled front surfaces 312 and 314 combine toimpart a selected compression force F on the elastomeric member 236 toplace the elastomeric member 236 into sealing engagement with both thestationary seal ring surfaces 224, 226 and 218 and the outer gland platesurface 76. The angled front surfaces 312 and 314 of the compressionplate 300 generate the compression force F having an axial componentwhich acts to bias the elastomeric member 236 into sealing contact withthe stationary seal ring 14 and a radial component which acts to biasthe elastomeric member 236 into sealing contact with the outer glandplate 36. A resultant compression force F′ is further imparted upon theelastomeric member 236 by the beveled surface 226 and the radiallyextending surface 224 of the stationary seal ring 14. Preferably, theangle of the front surface 312 to the front surface 314, as well as theangle of the surface 226 to the surface 224 of the stationary seal ring14, is such that the magnitude of the radial force imparted to theelastomeric member 236 is sufficient to sealingly seat the elastomericmember against the outer gland plate surface 236 without producingexcessive axial friction or drag forces between the elastomeric member236 and the outer gland plate. By limiting the drag forces between theelastomeric member 236 and the outer gland plate surface 236, mechanicalhysteresis or O-ring hysteresis of the elastomeric member is inhibited.In this manner, a fluid-tight and a pressure tight seal can bemaintained between the stationary seal ring 14 and the outer gland plate36 under a wide range of operating conditions, without unduly limitingthe axial motion of the stationary seal ring 14.

A significant advantage of the secondary sealing assembly 301 is thatthe elastomeric member 236 can seat against the stationary seal ring 14and the outer gland plate 36 without developing large frictional forcesbetween the elastomeric member and the gland plate that can inhibitaxial motion of the stationary seal ring, while concomitantlymaintaining sealing between the stationary seal ring and the outer glandplate. Additionally, the secondary seal assembly reduces the number ofseal components necessary to create an axial biasing force on thestationary seal ring 14. For example, the secondary sealing assemblydoes not require additional compliant parts that act in connection witha compression plate to squeeze the O-ring to form the appropriate fluidseal.

An alternative embodiment of the compression plate 300 is illustrated inFIG. 5C, in which the front surface 313 extends radially between theinner surface 304 and the connecting wall 310. In this embodiment, thefront surface 313 of the compression plate imparts a primarily axialcompression force on the elastomeric member 236. The beveled surface 226and the radially extending surface 224 of the stationary seal ring 14 inturn impart a compression force “F” that acts to place the elastomericmember 236 into sealing engagement with both the outer gland platesurface 76. The resultant compression force “F” includes an axialcomponent and a radial component which acts to bias the elastomericmember 236 into sealing contact with the outer gland plate 36 in amanner analogous to the first embodiment of the compression plate 300,described above. Alternatively, the compression plate can be providedwith two angled front surfaces and the stationary seal ring can beconfigured to include only a single radially surface for contacting theelastomeric member. In such an embodiment, the angled front surfaces onthe compression plate would impart both a radial and an axialcompression force on the elastomeric member.

In addition to the mechanical biasing provided by the mechanical springs270, an additional fluid biasing system is provided in the seal 10 ofthe present invention. With reference to FIGS. 1, 5A and 5B, the fluidbiasing system includes the radially extending fluid bore 240 whichintroduces barrier fluid to the rear surface 220 of the stationary sealring 14 to provide a closing force on the stationary seal ring 14. Afluid-tight and pressure-tight annular closing fluid chamber 280 isformed between elastomeric members 94 and 236, the rear surface 220 ofthe stationary seal ring 14 and the third axially extending surface 74of the outer gland plate 36.

As best illustrated in FIGS. 5B and 14A, a closing fluid at a regulatedpressure is provided from a fluid supply (not shown) to a closing fluidchamber 280 through input fluid bore 240. The fluid is preferably a gas.The fluid within the chamber exerts a fluid closing force F_(b) on thestationary seal ring. The fluid closing force F_(b) operates incombination with the mechanical spring closing force F_(s), and aprocess fluid force F_(p), due to the process fluid pressure acting uponthe first annular connecting wall 210 of the stationary seal ring 14, toform a combined total closing force F_(c) to bias the seal face 18toward the seal faces 20 a and 20 b in a sealing relationship.Preferably, the sum of the fluid closing force F_(b), the mechanicalspring closing force F_(s), and the process fluid force F_(p) balancesthe total separation or opening force F_(o) formed at the seal faces tocontrol the separation of the seal faces 18 and 20. In this manner, overseparation of the seal faces, which can potentially result in excessivefluid leakage, can be inhibited. In addition, seal face contact can beminimized at all rotation speeds to reduce frictional wear of the sealfaces.

The magnitude of the fluid closing force F_(b) can be adjusted orregulated by controlling the pressure of the closing fluid within theclosing fluid chamber 280. The ability to adjust the closing force F_(b)acting on the rotary seal ring provides for significant advantages. Forinstance, the magnitude of the closing force F_(b) can be varied tomaintain a sealing relationship between the seal faces 18 and 20 in theevent of a change in operating conditions. In the particular embodimentdescribed herein, the closing force is dependent upon the opening forcebecause the barrier fluid is employed as the closing fluid.Consequently, the mechanical seal 10 in combination with a feedbacksystem can dynamically regulate the fluid seal and/or the gap formedbetween the seal faces 18, 20 to control the amount of leakage duringoperation. A suitable feedback system is described in detail below.

The illustrated fluid biasing system, which includes the axial bore 228and the groove 180, provides a simple integrated system that controlsthe amount of separation of the seal faces to regulate the fluid sealformed between the seal faces. Accordingly, the system can operate incombination with the separation or opening force F_(o) provided bybarrier fluid introduced to the seal faces 18, 20 to adjust the degreeof seal face contact. Hence, the mechanical seal 10 can regulate oradjust the seal face separation, as well as the fluid seal formedtherebetween, over a wide range of operating conditions. This increasesthe flexibility of the seal and allows the seal to be used in multipleenvironments.

One skilled in the art will recognize that the seal is not limited tothe specific fluid closing system described herein and that alternativefluid closing system arrangements are possible. For example, separatefluid supplies can be used to supply barrier fluid to the seal faces andto supply closing fluid to the rear surface of the stationary seal ring.Those of ordinary skill will recognize that the barrier fluid, processfluid, or some other fluid can be used as the closing fluid.Furthermore, either the mechanical springs 270 or the closing fluidsystem can be used as the sole source of axial biasing force,eliminating the need for the other axial closing force.

Referring to FIGS. 14A and 14B, the total opening force F_(o) thatoperates in opposition to the closing force F_(c) includes the sum oftwo forces: F₁ which corresponds to the hydrostatic force formed betweenconcentric seal face 20 a and the stationary seal ring face 18, and theforce F₂, which corresponds to the combined hydrostatic and hydrodynamicforces formed between the seal faces 20 b, when defined to include thegrooves 20 b, and the seal face 18. According to a preferred practice,the barrier fluid introduced to the seal faces 18, 20 through the fluidbiasing system exerts a primarily hydrostatic lifting force, F₁, on thefirst seal face 20 a, as well as on the corresponding portion of theseal face 18, that operates to separate at least a portion of thestationary seal ring face 18 from at least a portion of the rotary sealring first face 20 a to form a gap h_(o) therebetween. The magnitude ofthe primarily hydrostatic separation force F₁ acting upon seal face 20 aand the seal face 18 is at least partially dependent upon the magnitudeof the pressure differential between the barrier fluid pressure P_(b)and the process fluid pressure P_(p) across the seal face 20 a. Thehydrostatic separation force F₁ decreases from a maximum value at theouter radial edge of the spiral grooves 180, where the fluid pressurebetween the seal faces is equal to the barrier fluid pressure P_(b), toa minimum value at the outer radial edge of the rotary seal, e.g., atthe intersection of the first seal face 20 a and the outer surface 172.At this point, the fluid pressure between the seal faces is equal to theprocess fluid pressure P_(p). The force F₁ acts upon the areas of theseal faces that overlap the first connecting wall 210 of the stationaryseal ring 14, i.e., the annular seal face portion that extends radiallyoutward from line D. The hydrostatic separation force F₁ is independentof, and thus does not change as a function of, the speed at which theshaft 12 and thus the rotary seal ring 16 rotates.

The barrier fluid introduced through the axial bore 228 to the grooves180, and thus to the seal faces 18, 20, exerts a hydrodynamic liftingforce F₂ thereon. The force F₂ acts upon a portion of the concentricseal face 20 b, when defined to include the grooves 180, as well as onthe corresponding portion of the seal face 18, to separate at least aportion of the stationary seal ring face 18 from at least a portion ofthe rotary seal ring second face 20 b to form a gap therebetween. Thelifting force F₂ includes both hydrostatic and hydrodynamic components.The magnitude of the separation force F₂ acting upon the second sealface 20 b and on the seal face 18 is dependent upon at least twofactors: the pressure differential between the barrier fluid pressureP_(b) and the ambient fluid pressure P_(a) across the seal face 20 b(the hydrostatic component); and the velocity at which the rotary sealring seal face 20 b rotates relative to the stationary seal ring face18, i.e., the shaft rotation speed (the hydrodynamic component). Theprimarily hydrostatic lifting force F₁ and the combination hydrostaticand hydrodynamic lifting force F₂ combine to produce the opening forceF_(o) on the seal faces 18 and 20.

The gap formed by the opening force F_(o) is maintained at apredetermined thickness h_(o), or is adjustable, to both minimizeleakage across the seal faces and separate the seal faces to reducewear, as illustrated in FIG. 14A. The predetermined gap thickness h_(o)is maintained by the unique balancing system provided by the seal 10 ofthe present invention in which the opening force F_(o) on the seal faces18 and 20 is balanced by the closing force F_(c). The closing forceF_(c) includes the process fluid force F_(p), which acts upon the firstconnecting wall 210 of the stationary seal ring 14; the barrier fluidclosing force F_(b), which acts upon the rear surface 220 and the secondconnecting wall 222 of the stationary seal ring 14; and the mechanicalspring closing force F_(s), which also acts upon the second connectingwall 222 of the stationary seal ring 14.

During operation, the opening force F_(o) is balanced by the closingforce F_(c) to maintain the gap at a preferred standard thickness h_(o).The magnitude of the lifting force F₂ on the second seal face 20 b whenthe gap is at the preferred thickness h_(o) is illustrated by solid lineA in FIG. 14A. The curved portion of the line A represents thehydrodynamic component of the lifting force F₂, and has a maximum valuethat corresponds to the location of the highest pressure fields withinthe groove 180. If a change in operating conditions results in thethickness h of the gap decreasing below the preferred value h_(o)(h<ho), represented by alternately dashed line B, the balancingarrangement of the seal 10 of the present invention compensates byreturning the gap to the preferred value h_(o). This occurs since adecrease in the gap thickness results in an increase in the hydrodynamiccomponent of the lifting force F₂, as illustrated by line B. Theresulting increase in the lifting force F₂ causes the seal faces toseparate until the preferred gap thickness h_(o) is again reached.

Likewise, if a change in operating conditions results in the thickness hof the gap increasing above the preferred value h_(o) (h>h_(o)), thebalancing arrangement of the seal 10 of the present inventioncompensates by returning the gap to the preferred value h_(o).Specifically, the increase in the gap thickness results in a decrease inthe hydrodynamic component of the lifting force F₂, as illustrated bydashed line C in FIG. 14A. The resulting decrease in the lifting forceF₂ causes the seal faces to come together until the preferred gapthickness h_(o) is again reached.

Additionally, the mechanical seal 10 of the present invention allows forthe adjustment of the degree or elimination of direct, frictionalcontact between the seal faces, independent of shaft rotational speed,by adjusting the barrier fluid pressure, and thus the magnitude of thehydrostatic lifting force F1, to produce the desired separation gap.

FIG. 14B illustrates the ability of the mechanical seal 10 to adjust,regulate, or change the opening force F_(o) as a function of thedifference between the pressure of two system fluids, for example, thedifference between the barrier fluid pressure P_(b) and the processfluid pressure P_(c). Additionally, the effects of increasing theclosing fluid pressure on the stationary seal ring of the mechanicalseal 10 during low speed shaft rotation is also shown. As illustrated,increasing the barrier fluid pressure from P_(b1) to P_(b2) results in acorresponding increase in the closing force F_(c) along the portions ofthe stationary seal ring that are exposed to the closing fluid,designated as E. The closing force portion F_(p) does not increase alongthe outer radial portion of the stationary seal ring 14, whichcorresponds to the first connecting wall 210, since the O-ring 94isolates that outer portion of the stationary seal ring from the closingfluid and thus is only exposed to the process fluid pressure.

The increase in barrier fluid pressure from P_(b1) to P_(b2) within thegrooves 180 and thus between the seal faces 18, 20 results in anincrease in the opening force F_(o) along the entire radial surface ofthe seal faces, as illustrated in FIG. 14B by the force lines F₁₁ andF₂₁, which correspond to the initial barrier fluid pressure P_(b1), andby the force lines F₁₂ and F₂₂, which correspond to the increasedbarrier fluid pressure P_(b2). The increase in the opening force fromF21 to F22 in the hydrodynamic and hydrostatic region of the seal (e.g.,other than from line D to the outer diameter of the seal rings)generally corresponds to the increase in closing pressure from Fb1 toFb2, However, the increase in opening force from F11 to F12 is notoffset by a corresponding increase in the closing force of Fp. Moreparticularly, the portion of the increased primarily hydrostatic liftingforce F₁₂ applied to the seal face 20 a and that portion of seal face 18that is radially aligned with the first connecting wall 210 of thestationary seal ring 14, is not balanced by a corresponding increase inthe closing force. This occurs because the first connecting wall 210 ofthe stationary seal ring 14 forms part of the process fluid chamber 295and as such is exposed solely to the process fluid, and not to thebarrier fluid. This unique arrangement thus allows for the opening forceF_(o) only to be increased along the outer radial portion of the sealfaces, e.g., from line D to the outer diameter of the seal rings, solelyby increasing the barrier fluid pressure. Since this portion correspondsto the hydrostatic region along concentric seal face 20 a, the increasedopening force is independent of shaft rotation speed.

Another advantage of the illustrated seal 10 is that it can continue tooperate even when a loss of barrier fluid pressure supplied to the sealfaces 18, 20 occurs, as illustrated in FIG. 15. A hydrostatic openingforce F_(o) is generated between the seal face 18 and 20 a due to thepressure difference between the process pressure P_(b) and the ambientpressure P_(a). The hydrostatic opening force Of is opposed by a closingforce F_(c) composed of a process fluid force component F_(p) and aspring force component F_(s). The spiral grooves no longer produce ahydrodynamic lifting force because of the absence of barrier fluidwithin the grooves. The relatively large pressure differential thatforms between the outer diameter region, which is exposed to the processfluid, and the inner diameter region, which is exposed to ambient, doesnot transport or pump undesirable levels of process fluid across theseal faces to the ambient side of the seal because of the fluid barriercreated between the seal faces by the hydrostatic clamping force. Uponloss of barrier fluid the seal thus operates as a partial contact liquidseal.

The mechanical seal 10 of the present invention can include a pressurefeedback system that regulates either or both of the closing pressureand the pressure of the barrier fluid supplied to the seal to maintainthe desired conditions at the seal faces 18, 20 of the seal rings 14,16. The pressure control system can include pressure sensors mountedwithin or at the seal to monitor changes in barrier and closing fluidpressure during operation. The pressure sensors can be coupled to acontroller or the like in a closed or open feedback system for adjustingthe barrier and/or closing fluid pressure in response to pressurevariations due to changes in operating conditions. Examples of pressurefeedback systems are disclosed in U.S. Pat. No. 2,834,619 and U.S. Pat.No. 3,034,797, both of which are incorporated herein by reference.

Alternatively, a pressure feedback system can employ one of the systemfluids, such as barrier, process or closing fluid, as a regulator fluidinput and regulate either the barrier fluid pressure or closing forcebased on this regulated input. In doing this, the pressure feedbacksystem can sense a change in pressure between selected fluid pressuresand corrects any imbalance. The pressure feedback system accomplishesthis correction by connecting the system to a high pressure fluid supplyto add fluid to the system to raise the pressure therein or to ventpressure from the system when internal pressure is above a selectedvalue. Such pressure feedback systems 400 are illustrated in FIGS. 12and 13.

FIG. 12 illustrates one embodiment of a fluidic feedback pressureregulating system 400 suitable for use with the mechanical seal 10. Thefeedback system 400 is preferably employed to regulate a system fluidbased on the pressure of another system fluid. According to onepractice, the system initially sets the barrier fluid pressure at aselected level relative to the process pressure by a selected amountcorresponding to a spring pressure. The barrier pressure is thenemployed as a system output regulated fluid that operates as a systemfluid sensor to selectively add a closing fluid to the system 400. Theregulated closing fluid corresponds to the closing fluid contained inthe closing fluid biasing system discussed above.

The illustrated feedback system 400 is preferably sized and dimensionedfor mounting within the inner and outer gland plates 34 and 36. Thesystem is coupled to the seal 10, whose components have been previouslydescribed. Therefore, like reference numerals designate like parts. Thestationary seal ring 14 includes axial bore 228 that communicates at oneend with stationary seal face 18 and at the other end with a barrierfluid source. The rotary seal ring 16 has a pumping groove 180 formedtherein and which is positioned to directly fluidly communicate with theaxial bore 228. The groove and axial bore operate to channel a barrierfluid directly to the seal faces, between which a hydrodynamic liftingforce is created that separates the faces to form a gap therebetween.

The illustrated feedback system 400 employs a movable differentialpressure valve 408 disposed within an appropriately sized chamber formedwithin the glands 34 and 36. The movable valve 408 can include a numberof different valves including, but not limited to, spool or shuttlevalves, poppet valves, needle valves, diaphragms, bellows, and otherlike movable valves that are capable of conveying or being acted upon bya pressurized fluid. The chamber mounts an annular fluid manifold 414that is bored in a selected manner to allow communication between thevarious pressure passages and bores of the fluidic feedback pressureregulating system. The illustrated fluid manifold 414 has a central borethat seats the movable valve 408. The bore is sized slightly larger thanthe outermost diameter of the movable valve to allow relatively freeaxial movement of the valve within the bore between open and closedpositions. The fluid manifold 414 includes a number of radiallyextending fluid bores 410 and 412 to allow the manifold to selectivelycommunicate a particular pressurized fluid to the gland chamber. Sealingstructures such as O-rings 422 and 424 are mounted within correspondinggrooves formed in the outer surface of the manifold to form a pressureand fluid seal between the inner walls of the chamber and selectedportions of the fluid manifold 414.

The movable valve 408 divides the chamber into an input fluid chamber402 and an output fluid chamber 403, with an intermediate chamber 413formed between the flanged end portions of the valve. The valve 408 iscoupled to an adjustable spring 404, one end of which is attached to amanually adjustable screw 406. The illustrated adjustable screw 406 ismounted in a limited access location to prevent or inhibit personnelfrom tampering with or adjusting the spring tension from a factorypre-set setting. If necessary, the system operator can adjust the springtension by accessing and then turning the screw in a selected manner.The screw 406 and the spring 404 thus act in combination to help definean initial or set point pressure for the illustrated pressure regulationsubsystem 400.

The screw 406 and spring 404 extend into the input fluid chamber 402from the interior surface of the gland. The input fluid chamber 402 cancommunicate with a process fluid distribution network to allow theprocess fluid of the seal to communicate with the input regulationchamber 402, as designated. The process fluid distribution network ofthe fluidic feedback pressure regulation system 400 can include, amongother structure, appropriate process fluid chambers formed within orabout the mechanical seal, such as process fluid chamber 290 and processfluid bore 421 (shown in phantom) that communicates the process fluidfrom the chamber 290 to the input fluid chamber 402. Those of ordinaryskill will recognize that the process fluid distribution network caninclude that collection of internal bores and passages formed within thegland to enable the process fluid to communicate, if desired, with themovable valve 408 in a selected manner. The regulation system can alsoemploy couplings external of the gland to communicate system fluids withparticular portions or components of the system. For example, externalfluid conduits can be connected to the gland to transfer the processfluid from the fluid housing to the input process fluid bore 421.

With further reference to FIG. 12, the fluidic feedback pressureregulation system 400 can also include a barrier fluid distributionnetwork that communicates barrier fluid from a high pressure barrierfluid supply (not shown) to the fluid manifold 414. The barrier fluiddistribution network can include appropriate barrier fluid passages thatcommunicate the barrier fluid from the gland chamber to a separateportion of the seal, including to the barrier fluid biasing system,i.e., axial bore 228 and groove 180, to other feedback systems that canbe mounted within the gland, and to other fluid passages/bores such asfluid supply 420 and barrier passage 430. The movable valve 408 definesan intermediate chamber or channel 413 which can communicate with abarrier fluid source through input supply bore 420 and input chamberbore 410. The intermediate chamber 413 is also selectively disposed influid communication with the barrier fluid distribution network by wayof output barrier bores 412 and 240.

During operation, the process fluid from the housing 11 communicateswith the input chamber 402 through the process fluid distributionnetwork. According to one practice, the process fluid is directed fromthe process chamber 290 to the input chamber 402 through the inputprocess pressure bore 421. The process fluid is at a given operatingpressure. The process fluid in the input fluid chamber 402 exerts apressure on the input side, e.g., the left side, of the movable valve408. In addition, the adjustable spring 404 exerts a pressure on themovable valve 408. The combination of these two forces or pressuresforms the input pressure, which exerts an initial input axial force thatbiases the movable valve 408 to the right.

The barrier fluid source introduces the barrier fluid to the fluidicfeedback pressure regulating system and to the mechanical seal by thebarrier fluid distribution network. The barrier fluid from the barrierfluid source is selectively introduced through the input supply passage420 to the input barrier bore 410 and into the intermediate chamber 413.The barrier fluid is then selectively introduced to the output chamber403 by selectively biasing the movable valve 408 between open and closedpositions. The valve 408 is illustrated in the closed position.

The barrier fluid housed in the output fluid chamber 403 exerts anopposite or axially inward pressure against the right side of themovable valve 408 to form an output pressure. When the output pressureexerted by the barrier fluid is less than the sum of the process fluidpressure and the adjustable spring pressure, the differential pressurevalve 408 moves to the right into the open position. This enables theintermediate chamber 413 to communicate with the output barrier bore 412to provide a fluid pathway from the barrier fluid supply through thefluid supply conduit to the output fluid conduit 412. The barrier fluidthen passes through the passage 240 into the axial bore 228, and henceto the remainder of the barrier fluid distribution network. The passage240 further pressurizes the closing chamber 280.

As the barrier fluid distribution network fills with barrier fluid fromthe supply source, the barrier fluid pressure in the output fluidchamber 403 increases until the pressure equals or exceeds the sum ofthe pressures exerted by the process fluid and the adjustable spring404. When this occurs, the valve 408 is biased into the illustratedclosed position to disconnect the barrier fluid supply from the outputbarrier passage 240. The barrier fluid within the fluidic feedbackpressure regulation system is thus pressurized to a level equal to aboutthe sum of the pressures exerted by the process pressure and thevariable pressure of the spring 406.

The illustrated system 400 can further include a subsystem for ventingthe closing fluid from the closing fluid network. The subsystem caninclude most of the same components as the illustrated subsystem 400,except for the process fluid bore 421 and the barrier fluid bore 240.The subsystems can thus be utilized together or in any combination tocontrol a particular fluid pressure that acts upon, either directly orindirectly, the seal faces 18 and 20. The illustrated subsystem 400 canalso be employed to selectively connect a closing fluid supply (notshown) to the closing force biasing system of the seal independent ofthe barrier fluid system. The closing fluid system applies a closingforce to the backside of the stationary seal as a function of thepressure within the barrier fluid distribution network and/or thebarrier fluid biasing system, e.g., the axial bore 228 and groove 180.

The closing fluid distribution network of the subsystem connects thesource of closing fluid to the stationary seal ring 14. The closingfluid network exerts a closing axial biasing force on the seal ring 14to adjust or regulate the separation between the stationary and rotaryseal rings 14, 16. The closing fluid distribution network can includeany suitable arrangement and number of fluid conduits and bores thatintroduces the fluid to at least one of the seal rings to adjust theseparation therebetween. In particular, the illustrated network caninclude one or more of the input closing force supply passage 420, theinput closing fluid bore 410, the intermediate chamber 413, the outputclosing fluid bore 412, the closing fluid passage 240, and the closingfluid chamber 280. In the illustrated system 400, the barrier fluidsystem and the closing fluid distribution network share many of the samepassages/bores. Consequently, a discrete and dedicated series of fluidlyconnected passages can be employed to simultaneously pressurize thebarrier fluid system and closing fluid network. According to a preferredpractice, the closing fluid can be any suitable barrier fluid.

FIG. 13 illustrates another embodiment of the fluidic feedback pressureregulation system 401 of the present invention. The illustrated system401 employs a diaphragm D as the movable valve. According to onepractice, the system 401 preferably disposes the input barrier fluidpressure at a selected level relative to the process fluid pressure andthe pressure provided by the spring 454, while concomitantly adding aclosing fluid to the system. The operation and function of theillustrated system 401 is similar to the operation of the feedbackregulating system 400 of FIG. 12. Like reference numerals refer tosimilar parts in the Figures.

The gland plates 34 and 36 are bored to form a pair of chambers 470 and471 that are axially spaced from each other. The chambers areselectively disposed in fluid communication with each other. Thediaphragm D is sized and dimensioned to mount within the chamber 470 anddivides the chamber into an input fluid chamber 402 and an output fluidchamber 403. The diaphragm D has a bellows portion 480 and an axiallyextending spindle portion 481 that has a central bore which is open atboth ends. The illustrated diaphragm D is coupled to a spring 454, oneend of which is attached to a manually adjustable screw 456. The screw456 includes a head portion 456A which is mounted along the innersurface of the gland at a limited access location. An annular O-ring 457mounts about the head 456A in a groove to provide a fluid seal betweenthe external environment and the chamber 470. The screw variably adjuststhe tension of the spring to either increase or decrease the tension andtherefore the pressure of the spring, while concomitantly increasing thepressure within the input chamber 402. The screw 456 and the spring 454thus act in combination to define the initial or set point pressures inthe illustrated pressure regulation subsystem 401. The limited accesslocation of the screw inhibits or prevents a system operator fromadjusting the spring tension, which can be pre-set to a selected tensionat the factory. Those of ordinary skill will also recognize that themanually adjustable screw 456 can be mounted along the outer surface ofthe gland.

The screw 456 and spring 454 extend into the input fluid chamber 402from the axial inner surface of the inner gland plate 34. The inputfluid chamber 402 communicates with a process fluid distribution networkto allow the process fluid of the seal to communicate with the inputchamber 402. The process fluid distribution network of the fluidicfeedback pressure regulation system can include appropriate processfluid chambers formed within or about the mechanical seal, such asprocess fluid chamber 290, and input process fluid passage 462 (shown inphantom) that communicates the process fluid from the chamber 290 to theinput fluid chamber 402. Those of ordinary skill will recognize that theprocess fluid distribution network can include any suitable collectionof internal bores and passages formed within the gland that enables theprocess fluid to communicate with the diaphragm in a selected manner.The regulation system can also employ couplings external of the gland tocommunicate system fluids with particular portions or components of thesystem. For example, external fluid conduits can be connected to thegland to transfer the process fluid from the fluid housing to the inputprocess fluid bore 462. In an alternate embodiment, the gland can beinternally bored to allow the process fluid to communicate with theprocess fluid bore completely within the gland without the use ofexternal fluid couplers.

The chamber 471 is formed axially outward relative to the chamber 470.The chamber 471 further communicates on one side with the input fluidsupply passage 420. The chamber 471 mounts a spring biasing assembly 469having a spring 472, an intermediate plate 473 having a U-shapedcross-section, and a fixed annular sealing plug 474. One end of thespring 472 seats at the axially outermost portion of the chamber 471,the other end of which seats within a recess formed in the plate 473.The intermediate plate 473 has a sealing surface 473A that abuts aseating surface 475 formed on one end of the sealing plug 474. Thesealing plug 474 has an annular groove that mounts an O-ring 476 thatprovides a fluid seal between chambers 470 and 471. The plug preferablyhas a shoulder portion 477 that seats in a mating groove formed in thechamber wall to rigidly and fixedly seat the plug 474 in place. The plughas a central bore 477 that is sized to slidingly seat the spindleportion 481 of the diaphragm D. The plug operates to prevent fluidsupplied to the chamber 471 from the fluid passage 420 fromcommunicating with the output chamber 403 when the plate is in intimatefacing contact with the seat 475.

The illustrated intermediate plate 473 is alternately disposable betweenopen and closed positions by selected fluid and mechanical forces. Whenthe spring biasing assembly 469 is disposed in the illustrated closedposition, the sealing surface 473A contacts in a sealing relation withthe seat surface 475 of the plug 474. This position prevents fluidcontained in the chamber 471 from communicating with the output chamber403. When the assembly 469 is disposed in the open position, the plate473 is axially spaced from the plug 474 to allow the fluid withinchamber 471 to pass through the central bore 477 into the output chamber403.

With further reference to FIG. 13, the axial spindle 481 has an outerend that seats, in a closed position, against the sealing surface 473Aof the intermediate plate 473. When disposed in an open position, thespindle disengages from the sealing surface 473A, thus allowing fluid inthe output chamber 403 to communicate with the chamber 402 through thespindle's central bore.

In the illustrated system 401, the input fluid chamber 402 is fluidlyconnected to the process fluid chamber 290 via process fluid bore 462.The output fluid chamber 403 is fluidly connected to the barrier fluiddistribution network and the closing fluid network via fluid bore 240.The fluidic feedback pressure regulating system of the inventionincludes a barrier fluid distribution network that communicates barrierfluid from a high pressure barrier fluid supply to the diaphragm and/orto the barrier fluid biasing network. Further, the system includes aclosing fluid network that communicates a closing fluid, such as barrierfluid, to the closing fluid chamber 280.

During operation, the process fluid from the fluid housing communicateswith the input chamber 402 through the input process pressure passage462 and any other appropriately formed passageway within the seal and/orgland that enables the process fluid to enter the input chamber 402. Theprocess fluid is at a given operating pressure. The process fluid in theinput fluid chamber 402 exerts a pressure on the input side, e.g., theleft side, of the diaphragm D. In addition, the adjustable spring 454exerts a pressure on the diaphragm D. The combination of these twoforces or pressures forms the input pressure, which exerts an initialinput axial force that biases the diaphragm towards the right.

The barrier fluid from the barrier/closing fluid supply (not shown) isintroduced to the regulation system 401 and to the mechanical seal 16 bythe barrier fluid distribution network. According to one practice, thebarrier fluid from the barrier fluid supply is selectively introduced tothe feedback system, and in particular to the output chamber 403 throughsupply bore 420. Consequently, the position of the intermediate plate473 determines whether barrier fluid is introduced to the output chamber403. The barrier fluid housed in the output fluid chamber 403 exerts anopposite or axially inwardly pressure against the right side of thediaphragm D to form the output pressure.

When the input pressure exerted by the process fluid and the spring 406is greater than the output pressure within the output chamber 403, thediaphragm D moves to the right, and the spindle 481 separates the platesurface 473A from the seat surface 475. The fluid supply introducesbarrier fluid to the chamber 471, which then passes through the centralbore 477 of the plug 474 to the output chamber 403. The barrier fluidthen passes therefrom to the output passage 240 and into the axial bore228 and the chamber 280.

As the barrier fluid distribution network fills with barrier fluid fromthe supply, the barrier fluid pressure in the output fluid chamber 403increasingly exerts a pressure on the diaphragm D to force it in theopposite direction, e.g., to the left. When the barrier fluid pressurewithin the output chamber 403 generally equals the sum of the pressuresexerted by the process fluid and the adjustable spring 454, thediaphragm D is forced to the left. The spring 472 and the intermediateplate 473, in combination with the barrier fluid pressure within thechamber 471, forces the plate sealing surface 473A back into contactwith the seat 475, thereby disconnecting the fluid supply from theoutput chamber 403. The barrier fluid within the fluidic feedbackpressure regulation system 401 is thus pressurized to a level equal toabout the sum of the pressures exerted by the process pressure and theselectable pressure of the spring 454. Hence, the barrier fluid withinthe output chamber 403 is pressurized to a level above the process fluidby an amount corresponding to the tension or pressure of the spring 454.Those of ordinary skill will recognize that the increase in barrierfluid pressure within the output chamber 403 is indicative of lowbarrier pressure at the seal faces, and thus of impending seal facecontact. The addition of barrier fluid to the seal faces through theaxial bore 228 and the groove 180 pressurizes the gap at the seal facesto separate the seal faces.

In assembly, the rotary seal ring 16 is mounted onto the sleeve 100 byaligning the drive slots 138 of the rotary seal ring with axiallyextending drive pins 136, which extend from drive bore 134 of the holderassembly. The centering member 170 is concentrically disposed about thesleeve and is further placed into contact with the inner surface 166 ofthe rotary seal ring. Likewise, the O-ring 130 is disposed withinannular groove 128 formed in the sleeve 100 and is further placed insealing contact with the rear surface 174 of the rotary seal ring 16.

The stationary seal ring 14 and the compression plate 300 are mountedwithin the stationary seal ring receiving chamber 90 of the outer glandplate 36 by disposing the mechanical springs 270 within spring bores 272of the outer gland plate 36 to abut the rear surface 307 of thecompression plate 300. The axial section 230 of the fluid bores 228 andthe bores 316 of the compression plate 300 are aligned with theretaining pins 250 extending from the bores 252 formed in the outergland plate 36. The O-ring 236 is concentrically disposed about thesecond surface 76 of the outer gland plate and is placed into sealingcontact with the radial extending section 224 and beveled section 226 ofthe stationary seal ring 14. The surfaces 312 and 314 of the compressionplate bias the O-ring 236 into sealing contact with both the stationaryseal ring 14 and the outer gland plate 36. The O-ring 94 is disposedwithin groove 92 of the outer gland plate 36 and further placed intocontact with the second outer surface 208 of the stationary seal ring14. The O-rings 94 and 236 accordingly provide for fluid-tight andpressure-tight sealing between the outer gland plate and the stationaryseal ring 14.

One skilled with the art will recognize that alternative mechanicalspring arrangements are possible, including an arrangement without thecompression plate 300 in which the mechanical springs directly contactthe rear surface of the stationary seal ring 14.

Gland plate O-ring 56 is then mounted within gland gasket groove 70 andthe outer gland plates 36, the sleeve 100, and the stationary and rotaryseal rings 14 and 16 are concentrically disposed about the shaft 12. Thelock ring 144 is then concentrically disposed about the outer end 104 ofthe sleeve 100. Screws 142 are inserted through the lock ring intofastener receiving apertures 140 of the sleeve 100. The screws 142 aretightened into frictional engagement with the shaft 12, thereby securingthe sleeve 100, as well as the rotary seal ring 16, with the shaft 12.

The inner gland plate 34 is then concentrically disposed about theshaft. The flange 120 of the rotary seal ring sleeve 100 and the rotaryseal ring 16 are mounted within the inner gland plate 34. As shown inFIG. 1, the rotary seal ring 16 and the flange 120 of the sleeve 100 arespaced from the inner gland plate inner surface 38, thereby permittingrotation of the sleeve 100 and the rotary seal ring 16 relative to theinner gland plate 34. The gland plates 34 and 36 are next securedtogether by screws 84 that are mounted in and positively maintained byfastener-receiving apertures 82 in the gland plates. The gland gasketgroove 70 abuts radial extending surface 54 of the inner gland plate 34to provide a pressure-tight and fluid-tight seal between the glandplates 34 and 36.

Prior to fully securing the gland assembly 30 to the housing 11, theshaft 12, the sleeve 100, and the stationary and rotary seal rings 14,16 are centered within the gland assembly. An example of one type ofcentering mechanism is illustrated as centering clip 15, as shown inFIG. 1. Examples of other suitable centering mechanisms are described inU.S. Pat. No. 5,571,268, which is assigned to the assignee hereof andwhich is incorporated herein by reference.

After the seal 10 is assembled and mounted to the pump housing 11, theprocess medium is sealed within a process fluid chamber 290, as shown inFIG. 1. The process fluid chamber is defined by the inner gland plateinner surface 38, the outer gland plate second surface 68, O-rings 56and 94, the outer surface of the sleeve 100, the outer surface 172 ofthe rotary seal ring 16, and the first and second outer surfaces 206,208 and first connecting wall 210 of the stationary seal ring 14. Theambient medium, typically air, fills an ambient fluid chamber 295,typically sealed from the process chamber 290, that is defined by thestationary and rotary seal ring inner surfaces 162, 202, the O-rings 130and 236 and the outer surfaces 112 and 114 of the sleeve 100. The terms“ambient” and “ambient medium” are intended to include any externalenvironment or medium other than the process environment or processmedium.

Continuing to refer to FIG. 1, the O-ring 118 prevents the seepage ofprocess fluid along the shaft 12. The flat gasket 50 prevents theseepage of process fluid along the housing 11 and the seal 10 interface.The gland plate O-ring 56 prevents seepage of the process fluid betweenthe gland plate interface. The O-rings 94 and 130 prevent process fluidfrom invading the ambient fluid chamber 295 by way of the sleeve 100 andthe gland assembly 30.

In operation, barrier fluid is introduced to the spiral grooves 180 andthe seal faces 18, 20 a, 20 b through barrier fluid bores 228 in thestationary seal ring 14. The barrier fluid fills the gap formed betweenthe seal faces, thereby separating the seal faces 18 and 20 to form afluid seal between the process medium in the process chamber 290 and theambient fluid in the ambient fluid chamber 295. The gap is maintained ata predetermined thickness, or is adjustable, to minimize leakage acrossthe seal faces while concomitantly separating the seal faces to reducewear.

The effects of the barrier fluid on the seal 10 is twofold. First, thebarrier fluid can reduce wear on the seal faces by reducing the amountof direct, frictional contact between the seal face 18 and the sealfaces 20 a and 20 b, thus resulting in a longer life for the sealcomponents. Second, the barrier fluid operates to minimally transferheat generated by the direct, frictional contact between the seal facesaway from the seal faces, resulting in a more even temperaturedistribution throughout the seal 10 and thus prolonging the useful lifeof the seal components by reducing thermal stress that the componentsare subjected to.

The barrier fluid exerts a primarily hydrostatic lifting force on thefirst concentric seal face region 20 a, as well as on the correspondingportion of the seal face 18. The seal also develops a hybridhydrodynamic and hydrostatic force at the grooves 180 and along theinner concentric seal face 20 b. The barrier fluid exerts a liftingforce on the second seal face 20 b, as well as on the correspondingportion of the seal face 18, that operates to separate at least aportion of the stationary seal ring face 18 from at least a portion ofthe rotary seal ring face 20 b to form a gap therebetween.

A significant advantage of seal 10 of the present invention is that apair of concentric seal faces can be formed on a single seal ring, andpreferably on the seal rings of a non-contacting mechanical face seal.The formation of the concentric seals forms a dual seal design employingonly a pair of seal rings, although additional seal rings can be used ifnecessary. This forms a substantially compact mechanical seal, andpreferably a compact non-contacting mechanical face seal, that mounts toexisting fluid machinery in existing seal spaces, without requiringsignificant modification of the housing or of surrounding structure inorder to accommodate the mechanical seal.

Another significant advantage of the formation of a primarilyhydrostatic force along one portion of the rotary seal ring seal face 20and a combination hydrostatic and hydrodynamic force at another portionof the seal face is that the mechanical seal is capable of operating atrelatively low shaft speeds without promoting seal face wear. Further,the addition of the purely hydrostatic portion of the seal face,preferably along one of the concentric seal faces, enables the seal tomaintain a seal during barrier fluid loss. This advantage is realizedbecause the mechanical seal employs a balancing arrangement that enablesthe primarily hydrostatic seal region to form a substantial fluid sealbetween the process and ambient environments.

Still another significant feature is that the mechanical seal isarranged such that an increase or decrease in barrier fluid pressurerelative to the process fluid in the seal produces a corresponding netchange in the opening force that separates the seal faces only along thehydrostatic portion of the seal. This pressure arrangement enables thesystem operator to adjust the opening force by varying the pressuredifferential between the barrier fluid and the process fluid. Thispressure control feature allows substantially precise adjustment of thegap thickness during use.

Additionally, the mechanical seal 10 of the present invention allows forthe adjustment of the degree of contact or the thickness of the gapformed between the seal faces, independent of shaft rotation speed, byadjusting the barrier fluid pressure, and thus the magnitude of thehydrostatic lifting force F1, to produce the desired separation gap.Accordingly, it is possible to cause complete or partial separation ofthe seal faces at start-up, i.e., when the shaft is not rotating byincreasing the barrier fluid pressure. Likewise, complete or partialseparation of the seal faces can also occur at low shaft speeds byincreasing the barrier fluid pressure.

Still another advantage of the invention is that the secondary sealingstructure prevents, minimizes or inhibits seal face hang-up or O-ringhysteresis. Consequently, the seal exhibits increased sealing propertiessince the separation of the seal faces is maintained within systemlimits.

One skilled in the art will recognize that the seal 10 of the presentinvention can be designed as a completely split mechanical seal in whicha portion of each of the seal components, e.g. the gland assembly, thesleeve, the stationary and rotary seal rings, and the O-rings, is split.Such a split-seal design facilitates replacement or repair of damagedseal components by permitting installation and removal of the split sealcomponents without necessitating the complete breakdown of theassociated equipment, e.g., a pump or the like, and without having topass the seal over the end of the shaft. Examples of suitable split sealdesigns are described in U.S. Pat. No. 6,131,912, filed on Dec. 17,1997, and entitled “Split Mechanical Face Seal”, in U.S. Pat. No.6,068,264, filed on Dec. 17, 1997, and entitled “Split Mechanical FaceSeal with Negative Pressure Control System”, U.S. Pat. No. 6,059,293,filed on Dec. 17, 1997, and entitled “Split Mechanical Face Seal WithFluid Introducing Structure” and U.S. Pat. No. 6,068,265, filed on Dec.17, 1997, and entitled “Split Mechanical Face Seal With ResilientPivoting Member”, all of which are incorporated herein by reference.

One skilled in the art will recognize that, although only a single sealconfiguration is described and illustrated herein, the seal 10 of thepresent invention can be used in a dual or tandem or plural sealconfiguration in which multiple seals 10 or seal rings are arrangedaxially along the shaft.

It will thus be seen that the invention efficiently attains the objectsset forth above, among those made apparent from the precedingdescription. Since certain changes may be made in the aboveconstructions without departing from the scope of the invention, it isintended that all matter contained in the above description or shown inthe accompanying drawings be interpreted as illustrative and not in alimiting sense.

It is also to be understood that the following claims are to cover allgeneric and specific features of the invention described herein, and allstatements of the scope of the invention which, as a matter of language,might be said to fall therebetween.

Having described the invention, what is claimed as new and desired to besecured by Letters Patent is:
 1. A mechanical face seal for providingfluid seal between a housing and a rotatable shaft, the housing beingexposed to a process fluid, said seal comprising a first seal ringhaving a first seal face extending between an outer surface of saidfirst seal ring and an inner surface of said first seal ring, a secondseal ring having a second seal face, said first and second seal facesbeing opposed to one another, one of said first seal ring and saidsecond seal ring being adapted to rotate with said rotatable shaft, theother of said first seal ring and said second seal ring being restrainedfrom rotating, a plurality of pumping grooves formed in said first sealface, said plurality of pumping grooves receiving a barrier fluiddistinct from said process fluid introduced to said first and saidsecond seal faces, said plurality of pumping grooves generating apressure field between said first and second seal faces to separate saidseal faces during periods of shaft rotation, said plurality of pumpinggrooves being positioned between said outer surface and said innersurface of said first seal ring to form two concentric seal faces onsaid first seal face, and said second seal face being dimensioned toseat over said grooves and at least a portion of said two concentricseal faces when assembled, a closing fluid network to introduce aclosing fluid to a rear surface of said second seal ring to provide aclosing force on said second seal ring, said closing force acting upon aportion said second seal face overlapping said first portion of saidfirst seal face but not upon a portion of said second seal faceoverlapping said second portion of said first seal face to offset saidpressure field.
 2. The mechanical seal of claim 1, further comprising aplurality of axial passages formed within said second seal ring forintroducing said barrier fluid to a circumferential groove formed insaid second seal face, each passage opening onto said circumferentialgroove at one end and being in fluid communication with a fluid sourceat another end.
 3. The mechanical seal of claim 2, wherein saidcircumferential groove and said axial passages are in registration withat least a portion of said grooves formed on said first seal face suchthat said axial passages and said circumferential groove provide fluidto said grooves.
 4. The mechanical seal of claim 1, further comprising asleeve for securing one of said first seal ring and said second sealring to the rotatable shaft, said sleeve having a flanged end and beingsized for mounting generally concentrically about the rotatable shaft,and means for securing said sleeve to the shaft to rotate therewith. 5.The mechanical seal of claim 4, wherein said means for securing saidsleeve to said rotatable shaft comprises an annular lock ring mountedconcentrically about said sleeve and having a plurality of aperturesformed therein for receiving fasteners which frictionally engage therotatable shaft to secure said lock ring and said sleeve thereto.
 6. Themechanical seal of claim 1, further comprising a gland assembly sizedfor mounting to the housing and about the shaft and coupled to one ofsaid first seal ring and said second seal ring for connecting said oneof said seal rings to said housing.
 7. The mechanical seal of claim 6,wherein said gland assembly comprises an axially inner gland plate andan axially outer gland plate.
 8. The mechanical seal of claim 7, furthercomprising a resilient member interposed between said inner gland plateand said outer gland plate to form a seal therebetween.
 9. Themechanical seal of claim 1, further comprising a gland assembly coupledto said second seal ring for connecting said seal ring to said housing,a sleeve for securing said first seal ring to the rotatable shaft, saidsleeve having a flanged end and being sized for mounting generallyconcentrically about the rotatable shaft, and means for securing saidsleeve to the shaft to rotate therewith.
 10. The mechanical seal ofclaim 9, further comprising a resilient member interposed between asurface of aid second seal ring and said gland assembly to provide aseal between said second seal ring and said gland assembly, wherein saidsecond seal ring provides for axially and radially biasing saidresilient member into contact with said surface of said second seal ringand said gland assembly.
 11. The mechanical seal of claim 10, whereinsaid compression means comprises an annular compression plate having anannular inner flanged portion for engaging said resilient member. 12.The mechanical seal of claim 11, wherein said inner flanged portionincludes an axially and radially extending angled surface for axiallyand radially biasing said resilient method into contact with said secondseal ring and said gland assembly.
 13. The mechanical seal of claim 11,wherein barrier fluid received by said grooves generates a hydrodynamicand hydrostatic lifting force between a portion of said first seal faceand a portion of said second seal face to separate selectively at leastsaid portion of said first seal face from at least said portion of saidsecond seal face.
 14. The mechanical seal of claim 1, further comprisinga fluid control system for controlling said separation of said sealfaces by adjusting the pressure of the barrier fluid introduced to saidseal faces.
 15. A mechanical face seal for providing fluid sealingbetween a housing and a rotatable shaft, the housing being exposed to aprocess fluid, said seal comprising a first seal ring having a firstseal face, said first seal face having a first portion and a secondportion, a second seal ring having a second seal face, said second sealface being opposed to said first seal face, one of said first seal ringand said second seal ring being connected to said rotatable shaft torotate therewith, the other of said first seal ring and said second sealring being connected to said housing, a plurality of pumping groovesformed in said first portion of said first seal face for receiving abarrier fluid distinct from said process fluid and introduced betweensaid first portion and said second seal face and for producing ahydrodynamic fluid force and a hydrostatic fluid force between saidfirst portion and said second seal face to cause separation of at leasta portion of said first portion from at least a portion of said secondseal face, and a fluid conduit formed through said second seal ring,said fluid conduit having an opening at said second seal face forcommunicating with said plurality of pumping grooves to provide saidbarrier fluid to said grooves, and a closing fluid network to introducea closing fluid to a rear surface of said second seal ring to provide aclosing force on said second seal ring, said closing force acting upon aportion said second seal face overlapping said first portion of saidfirst seal face but not a portion of said second seal face overlappingsaid second portion of said first seal face.
 16. The mechanical seal ofclaim 15, further comprising a fluid control system for controlling saidseparation of said portions of said first and second seal faces byadjusting the pressure of the barrier fluid introduced to said sealfaces.